The present invention relates, in general, to an injection molding machine, and more particularly to an injection molding machine having a plasticizing unit and a closing unit of a type including at least one column completely traversing a supporting element and moveable relative thereto.
Injection molding machines, especially those for use under clean room conditions, are known to have modified sealing systems at the columns that move relative to the supporting element in order to decrease the release of contaminants. Examples of such sealing systems include seals made of Viton™ commercially available by DuPont Dow elastomers. The area stretching from the plasticizing unit to the mold mounting plate of injection molding machines, used under clean room conditions, are normally kept under a clean room environment having a lower class rating than the closing unit with the mold that are subject to a higher class rating. This difference in the class rating of the clean room environment is typically realized in practice by providing two separate spatial zones that are sealed from one another and include separate filtering systems. When maintenance work is required or the mold is to be replaced, the entire injection molding machine is moved into the area of lower class rating with respect to the clean room environment.
Still, contamination is encountered during operation as a result of abrasion caused by sliding friction as the column moves relative to the seal provided at the junction to the supporting element, and as a result of lubricant particles which evaporate from the lubricant film on the column. The relative movement between column and supporting element resembles a pump motion and promotes even more a spread of contaminations. Laboratory tests on closing units of an injection molding machine have shown that modified sealing systems, while decreasing the number of released contaminants at the point of penetration of the closing column into a fixed mold mounting plate, are still not sufficient to satisfy the more stringent demands on a clean room environment.
It would therefore be desirable and advantageous to provide an improved injection molding machine to obviate prior art shortcomings and to satisfy stringent clean room demands.